This guide to resolve any issues users get when they try to change nature or PID of a Pokemon from Gen 3 or Gen 4. DO NOT USE ANY POKEMON WITH MODIFIED PID ONLINE!
Foreword
The reason why people get various PID-Mismatch or Invalid Encounter type of messages, is because simply, they did not modify the Pokemon correctly.
In Generations 3 and 4, due to an in-depth understanding of how the Pseudo-Random Number Generator works (as well as game mechanics), the Personality Value (PID)